1. Field of the Invention
The present invention relates to a time-division multiple access (TDMA) communication system, and in particular, to a supervising and controlling system for at least one TDMA equipment in a communication station.
2. Description of the Prior Art
The TDMA communication system is a method for enabling a plurality of communication stations to communicate with one another through one repeater apparatus, and is employed especially in the field of satellite communication system.
In the TDMA system, a plurality of communication stations have respective time slots assigned thereto for communication between respective stations. Each station transmits its burst of communication in every time slots allotted thereto so that communication between respective stations can be performed on a time division basis without any time overlap of the signals transmitted from the various communication stations. In order to maintain such a time-division communication, it is essential for each station that its burst of communication is reliably controlled to be correctly transmitted in its own time slot. Each burst signal usually comprises a preamble burst portion and a data burst portion including sub-bursts.
In each communication station, a TDMA communication equipment usually has two first and second memories each storing transmission and reception burst signal control data (or burst time plan data) for designating a time position and a time length of each burst portions. The TDMA equipment operates under control by the burst signal control data stored in the first memory.
A parity code or an error detecting code is usually added to the burst signal control data in the prior art so that any error of the control data can be detected.
When an error is caused in the control data of the operating first memory by a certain reason, it is switched over to the second memory so that the TDMA communication can be maintained.
After switching over to the second memory, the content of the first memory must be rewritten into the correct burst signal control data so that the first memory stands by as a spare memory.
To this end, a known system has an apparatus for supervising and controlling the TDMA equipment. The supervisory and control apparatus periodically monitors the TDMA equipment, and upon detecting a control data error signal from the first memory after being switched to a spare one, the supervisory and control apparatus transfers the correct control data to the TDMA equipment so as to replace the contents of the first memory by the correct control data.
The supervisory and control apparatus also has a function to change the previous burst signal control data into new burst signal control data. When a change of the control data is required, the supervisory and control apparatus restrains the TDMA equipment from automatically switching over to the spare memory from the operating one, transfers the new control data to the spare memory, and thereafter designates the spare memory as a new operating one, with the previous operating memory being changed to a new spare one. Then, the TDMA equipment operates according to the new control data. Thereafter, the supervisory and control apparatus writes the new control data into the new spare memory, and then releases the restraint of the automatic switching from the operating memory to the spare memory.
In the known system, although it is automatically carried out at the TDMA equipment to switch over from an operating memory to a spare memory at a time when an error is caused in the burst signal control data of the operating memory, it is not performed at once to replace the damaged control data by the correct control data because the supervisory and control apparatus does not always monitor those memories. Accordingly, there is a problem that the TDMA equipment operates for a certain time period without any stand-by memory.
In a write-in operation of a burst signal control data into a memory, it can not be detected that the control data could not be transferred to the memory due to any damage of the transfer circuit. Therefore, the memory is handled as one storing the correct control data. Switching the memory to an operating one results in an interference of communication between respective stations in the TDMA communication system.